The present invention relates to the art of motor driven pipe cutting machines and, more particularly, to a portable, floor or bench supported pipe cutting machine in which the cutting action is manually controlled by the operator.
Motor driven pipe cutting machines of the character to which the present invention is directed are known and generally include a base or frame structure having rollers which support a pipe to be cut and a motor driven cutting wheel mounted on the frame for displacement into engagement with the pipe to cut the same. One such machine is shown, for example, in U.S. Pat. No. 2,553,147 to Roescheise wherein the cutting wheel is mounted on a pivotal lever which is displaceable toward a pipe to be cut by a hydraulic piston and cylinder unit through a motorized pump mounted on the machine frame. The pump is driven by an electric motor mounted on the frame and through a belt and pulley arrangement, and the cutting wheel is driven by the same electric motor and through a gear train having an input common with the pump drive. A pedal operated valve controls the flow of hydraulic fluid into the piston and cylinder unit to displace the cutting wheel into engagement with a pipe to be cut. When the foot pedal is released, the fluid circuit to the piston and cylinder unit is opened, the cutting wheel is spring biased away from the pipe and, unless the motor is turned off, the cutting wheel continues to rotate and the pump circulates hydraulic fluid in a bypass mode.
Use in the field of motor driven pipe cutters heretofore available is difficult as a result of the structural complexity and unitary construction of the pipe cutters. More particularly in this respect, the pipe cutter has to be transported to the point of use, such as in a truck, and then removed from the truck and setup on the ground or other underlying support surface for operation. The size and weight of the pipe cutter can make the loading and unloading thereof relative to the transport vehicle physically difficult for the workmen and require the use of special loading and unloading elevators or hoists as well as wheeled dollies or the like to facilitate ground transportation of the pipe cutter to the specific point of use. Other disadvantages of motor driven pipe cutters heretofore available, whether for use in the field or otherwise, include the limited ability of the operator to control the cutting force and thus the speed at which a pipe of given diameter can be cut. In the machine of Roescheise, for example, the operator only controls actuation of the pump and not the displacement thereof and, therefore, has no control of the cutting force or speed. In some pipe cutters, displacement of the cutting wheel is achieved by a hand operated lever which affords control of the cutting force by the operator, but such hand operation is physically fatiguing, whereby optimum force and cutting speed is likely to progressively decrease in connection with continuous use of the cutter by the operator.
Another disadvantage of prior pipe cutting machines resides in the difficulty in obtaining a quality cut and maintaining quality from one cut to another. In this respect, a quality cut requires that the axis of the pipe be maintained parallel to the axis of the cutting blade so that the cut is in a plane transverse to the pipe axis. Generally, the pipe to be cut is supported on rollers beneath the cutting blade and on an adjustable support spaced from the cutting machine. The latter support is adjusted laterally in an effort to align the pipe and cutting wheel axes, but the desired parallel relationship therebetween is extremely difficult to obtain and/or maintain from one cut to another. Any misalignment with respect to desired parallel relationship between the pipe and cutting wheel axes reduces the quality of the cut obtained, whereby considerable time and effort is spent to initially make the necessary adjustments of the adjustable support to assure as accurate alignment as possible, and frequent checking of the alignment is necessary in an effort to maintain the best possible alignment.
Yet another disadvantage in connection with pipe cutters such as that shown in the patent to Roescheise resides in the fact that there is a limited range of pipe diameters which can be safely cut. In this respect, the pipe is cradled between a pair of rollers which rotatably support the pipe during the pipe cutting operation, and it is important that the point of contact of the cutting wheel with the pipe at the beginning of the cutting operation is as close as possible to a vertical plane parallel to and between the roller axes. This relationship provides for the cutting force against the pipe to be fairly equally distributed between the supporting rollers. As the point of contact moves laterally away from the vertical plane, which occurs when the arm and blade are pivoted upwardly relative to the rollers to accommodate large diameter pipe, the cutting force is applied in a direction more toward one of the rollers than the other. As the diameter of pipe being cut increases such misdirection of force from the vertical plane progressively increases and this disadvantageously affects both the application of cutting force and the stability of the support for the pipe being cut, and the latter can result in the workpiece being displaced from the rollers by the rotating cutting wheel. In particular in this respect, it will be appreciated that as the pipe diameter increases the points of contact thereof with the rollers moves upwardly toward a plane tangential to the uppermost surfaces of the rollers, thus progressively decreasing the ability of the rollers to support the pipe against lateral displacement from its cradled position.